The present invention relates to a moisture-curing one-pack urethane adhesive composition. More particularly, the present invention relates to a moisture-curing one-pack urethane adhesive composition which has a good adhesive property to a painted steel and can be used, for example, for bonding automotive window glasses.
A moisture-curing one-pack urethane adhesive composition containing an urethane prepolymer as a main component is used for bonding automotive window glasses, said urethane prepolymer being, for example, a reaction product of a polyol and an excess of a polyisocyanate compound and having isocyanate groups at terminal ends of molecules. A method of bonding and mounting window glasses to an automotive body is adopted in which an adhesive composition is applied to the periphery of the window glasses and the applied window glasses are installed to body flanges. In this bonding process, a primer containing a polyisocyanate compound as a main component is usually used as a pretreating agent, but a process without any primer is needed from the viewpoint of the reduction of process steps.
However, it is difficult to bond the glasses without any primer to a painted steel coated with recent paints such as high solid paints, acid rain resistant paints, easy maintenance paints and the like.
Accordingly, the present inventors have intensively investigated in order to improve the adhesive property of the above moisture-curing one-pack urethane adhesive composition without any primer. As a result, it was found that a moisture-curing one-pack urethane adhesive composition having a good adhesive property to a painted steel is obtained by the use of a particular adhesive promoter and a particular curing catalyst.
Thus, the present invention provides a moisture-curing one-pack urethane adhesive composition comprising an isocyanate group-terminated urethane prepolymer as a main component, and
(1) a silane coupling agent as an adhesive promoter, and
(2) (a) 2,2xe2x80x2-dimorpholinodiethyl ether and/or di(2,6-dimethylmorpholinoethyl)ether, and (b) dibutyltin diacetylacetonate, as curing catalysts.
The moisture-curing one-pack urethane adhesive composition according to the present invention contains an isocyanate group-terminated urethane prepolymer as a main component. The urethane prepolymer may be prepared in a conventional manner by reacting various polyols with an excess amount of polyisocyanate compounds (usually, OH/NCO=1/1.5 to 1/4.0).
The above polyols include, for example, polyether polyols such as polyoxyalkylene polyols (referred to as PPG), modified polyether polyols and polytetramethylene ether glycols; polyester polyols such as condensed polyester polyols, lactonic polyester polyols and polycarbonate diols; polyols containing a main chain consisting of Cxe2x80x94C bonds such as acrylic polyols, polybutadiene polyols, polyolefinic polyols and saponified ethylene-vinyl acetate copolymers; other flame-retardant polyols, phosphorus-containing polyols, halogen-containing polyols and the like.
The above polyisocyanate compounds include, for example, tolylene diisocyanate (TDI), 4,4xe2x80x2m-diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), lysine diisocyanate, isopropylidene-bis(4-cyclohexylisocyanate), hydrogenated XDI and the like.
The moisture-curing one-pack urethane adhesive composition according to the present invention contains the above isocyanate group-terminated urethane prepolymer in an amount of 20 to 60% by weight, based on the adhesive composition as a whole.
The moisture-curing one-pack urethane adhesive composition according to the present invention contains a silane coupling agent as an adhesive promoter, in addition to an isocyanate group-terminated urethane prepolymer.
The above silane coupling agent includes, for example, epoxyalkylalkoxysilane, mercaptoalkylalkoxysilane, vinylalkylalkoxysilane, phenylalkoxyalkylalkoxysilane, isocyanatoalkylalkoxysilane, aminoalkylalkoxysilane and the like. Preferably, the silane coupling agent is mercaptopropyltrimethoxysilane, mercaptopropyl-methyldimethoxysilane, xcex3-N-phenylaminopropyltrimethoxysilane and/or xcex3-isocyanatopropyl-trimethoxysilane. The silane coupling agent may be present in an amount of 0.1 to 5% by weight, based on the total amount of the adhesive composition containing an isocyanate group-terminated urethane prepolymer and others.
Also, the moisture-curing one-pack urethane adhesive composition according to the present invention contains (a) 2,2xe2x80x2-dimorpholinodiethyl ether and/or di(2,6-dimethylmorpholinoethyl)ether, and (b) dibutyltin diacetylacetonate as curing catalysts, in addition to an isocyanate group-terminated urethane prepolymer and an adhesive promoter.
The 2,2xe2x80x2-dimorpholinodiethyl ether and/or di(2,6-dimethylmorpholinoethyl) ether may be present in an amount of 0.05 to 2.0% by weight, based on the total amount of the adhesive composition containing an isocyanate group-terminated urethane prepolymer and others. On the other hand, the dibutyltin diacetylacetonate may be present in an amount of 0.001 to 0.5% by weight, based on the total amount of the adhesive composition containing an isocyanate group-terminated urethane prepolymer and others.
A part of the isocyanate group-terminated urethane prepolymer contained in the moisture-curing one-pack urethane adhesive composition according to the present invention is preferably a hexamethylene diisocyanate derivative.
The above hexamethylene diisocyanate derivative includes, for example, biuret derivatives, isocyanurate derivatives and/or trimethylolpropane derivatives. The hexamethylene diisocyanate derivative may be present in an amount of 0.5 to 10% by weight, based on the adhesive composition as a whole.
The moisture-curing one-pack urethane adhesive composition according to the present invention may further contain plasticizers, fillers, solvents and the like, in addition to an isocyanate group-terminated urethane prepolymer, an adhesive promoter and curing catalysts.
The above plasticizers include, for example, di-isononyl phthalate, dioctyl phthalate (DOP), dibutyl phthalate, dilauryl phthalate, butyl benzyl phthalate, dioctyl adipate, di-isodecyl adipate, trioctyl phosphate, tris(chloroethyl) phosphate, tris (dichloropropyl) phosphate, a polyester of adipic acid and propylene glycol, a polyester of adipic acid and butylene glycol, an alkyl epoxystearate, an alkylbenzene, an epoxidized soybean oil and the like. The plasticizers may be present in an amount of 10 to 100% by weight, based on the adhesive composition as a whole.
The above fillers include, for example, calcium carbonate, silica, carbonblack, clay, talc, titaniumoxide, lime, kaolin, zeolite, diatomaceous earth and the like. The fillers may be present in an amount of 10 to 200% by weight, based on the adhesive composition as a whole.
The above solvents include, for example, xylene, toluene and the like. The solvents may be present in an amount of 0 to 20% by weight, if needed, based on the adhesive composition as a whole.
Also, if needed, the moisture-curing one-pack urethane adhesive composition according to the present invention may contain a tackifier (e.g. a titanate coupling agent), an antioxidant, a pigment or the like in a suitable amount.
The moisture-curing one-pack urethane adhesive composition according to the present invention can be prepared by adding in order an adhesive promoter, curing catalysts, plasticizers, fillers, solvents and other additives to an isocyanate group-terminated urethane prepolymer, and mixing them thoroughly.